Ca Films Research Articles

Transmittance and optical constants of Ca films in the 4-1000 eV spectral range.

The low expected absorption of Ca in the extreme ultraviolet (EUV) makes it an attractive material for multilayers and filters because most materials in nature strongly absorb the EUV. Few optical constant data had been reported for Ca. In this research, Ca films of various thicknesses were deposited on grid-supported C films and their transmittance measured in situ from the visible to the soft x-rays. The measurement range contains M2,3 and L2,3 absorption edges. Transmittance measurements were used to obtain the Ca extinction coefficient k. A minimum k of 0.017 was obtained at ∼23 eV, which makes Ca a promising low-absorption material for EUV coatings. A second spectral range of interest for its low absorption is below the Ca L3 edge at ∼343 eV. Measured k data and extrapolations were used to calculate the refractive index n using Kramers-Krönig relations. This is the first self-consistent data set on Ca covering a wide spectral range including the EUV.

Adsorption and sustained release of haemoglobin imprinted polysiloxane using a calcium alginate film as a matrix

Schematic representation of the fabrication procedure of the CA film based MIP.

API-X65の水素侵入挙動に及ぼす電析Ca皮膜の影響

API-X65の水素侵入挙動に及ぼす電析Ca皮膜の影響

Oxidation Kinetics of Calcium Films by Water Vapor and Their Effect on Water Vapor Transmission Rate Measurements

The oxidation of calcium films by water vapor is the basis of the “Ca test” used to measure low water vapor transmission rates (WVTRs) through gas diffusion barriers. The Ca test assumes that the Ca film oxidation rate is linear with H2O flux transmitted through the barrier. However, lag times are often observed during WVTR measurements that could indicate that the Ca film oxidation rate is not linear with H2O flux. To explore the oxidation kinetics of Ca films by H2O vapor, a new Ca test was developed based on quartz crystal microbalance (QCM) measurements. The QCM measures the mass gain that occurs as the Ca film oxidizes according to the reaction: Ca + 2H2O → Ca(OH)2 + H2. The QCM measurements observed a long lag time before the Ca films began to oxidize. The Ca film oxidation was studied using a number of experimental configurations. In all cases, the Ca film oxidation was not linear with H2O flux to the Ca film. These results suggest that the nonlinearity of Ca film oxidation in many WVTR experiments may result from the nonlinear oxidation of the Ca film itself. Additional measurements of the times required for complete Ca film oxidation versus H2O flux at constant temperatures were consistent with oxidation kinetics that were second-order in H2O flux. The nonlinear Ca film oxidation raises doubts about the validity of WVTR measurements using the Ca test. However, modeling based on the measured nonlinear Ca film oxidation kinetics suggests that the Ca test can yield reliable WVTR measurements under special circumstances. These circumstances occur when the accumulation volume between the barrier and the Ca film is small enough to allow for steady state pressure conditions where the H2O flux transmitted through the barrier is equivalent to the H2O flux removed by oxidation of the Ca film. The lag time is associated with the time required to obtain the steady state pressure in the accumulation volume.

Effects of substrate condition on calcium corrosion and its role in the calcium test for water vapour transmission rate

The electrical Ca test is a standard method for the estimation of the water vapour transmission rate through the encapsulation barriers. Here, we discuss the corrosion process of thin Ca films under different preparation conditions, and the impact of the substrate temperature. It is demonstrated that without vacuum drying of substrate, the Ca films corrode from the substrate side, even though they are encapsulated. The thickness dependence revealed its influence on lifetime, but not on its electrical properties. These observations reveal the strong impact of the Ca fabrication technology and measurement procedure on the corrosion process of Ca thin films.

Low-Temperature Growth Improves Metal/Polymer Interfaces: Vapor-Deposited Ca on PMMA

The controllable design of interfacial structures is of great importance in the applications of metal/polymer interfaces in a variety of technologies. The vapor deposition of Ca films on poly(methyl methacrylate) (PMMA) was studied as a prototype system to investigate the effects of substrate temperature on metal/polymer interfacial structure, using Ca adsorption microcalorimetry, sticking probability measurements, and X-ray photoemission spectroscopy. Earlier studies showed that when Ca vapor is deposited at room temperature, Ca atoms preferentially diffuse subsurface and react with the ester groups of PMMA at low coverage, leading to the formation of polymeric Ca carboxylates. As Ca coverage increases, the depth of the reacted polymer increases, so that diffusion of Ca through it to find unreacted esters gets slower, leading to an increase in the probability that Ca instead grows 3D Ca(s) particles on the surface, which eventually grow together into a continuous surface film. By deposition of metal vapo...

Effect of calcium and/or barium crosslinking on the physical and antimicrobial properties of natamycin-loaded alginate films

The preparation of alginate films with suitable properties requires a two-step contact with reticulating agents: initially a weakly structured pre-film is formatted which is further crosslinked in a second stage by immersion in a more concentrated solution. The present work evaluated the effects of a combined crosslinking procedure using calcium and barium ions on the physical and morphological properties of alginate-based films containing natamycin as antimicrobial agent. The release behavior of natamycin in water was evaluated as well as the antimicrobial activity against four target microorganisms, which are common cheese product contaminants. Films attributes were affected by the type of ion used in the second stage while the natamycin release rate and the antimicrobial activity were influenced by the ion used in the first stage. Films crosslinked with Ba2+ in the first and Ca2+ in the second stage (Ba–Ca films) exhibited physical properties very similar to films crosslinked with calcium in both stages. Release kinetics of natamycin in water fitted well to Fick's second law diffusional model, with effective diffusivity values ranging from 0.40 × 10−11 to 1.74 × 10−11 cm2/s. Ba–Ca films presented the lowest natamycin diffusion coefficient and the smallest inhibition zone diameter against the four microorganisms tested.

Calcium Thin Film Growth on Polyfluorenes: Interface Structure and Energetics

The adsorption of Ca vapor on two polyfluorenes, poly(9,9-di-n-hexyl-2,7-fluorene) (PDHF) and poly(9,9-di-n-hexyl-2,7-fluorene vinylene) (PDHFV), has been studied by adsorption microcalorimetry, low-energy He+ ion scattering spectroscopy (LEIS), and ultraviolet and X-ray photoelectron spectroscopies (UPS and XPS) at surface temperatures between 130 and ∼400 K. At 300 K, the initial heat of adsorption of Ca on PDHF is 250 kJ/mol and on PDHFV is 315 kJ/mol. We ascribe this initial heat to Ca reacting with impurities or defects in the polymers. The heat of adsorption for both polymers decreases nearly exponentially to the sublimation enthalpy of bulk Ca solid (178 kJ/mol) by 0.75 ML. The observed behavior is attributed to the increasing probability of Ca finding and adding to solid three-dimensional Ca islands which nucleate and grow on the polymer surface and eventually grow into a continuous solid Ca film on top of the polymer. LEIS, which shows only a slow increase of the signals related to solid Ca, supp...

Characterization of Sr-substituted hydroxyapatite thin film by sputtering technique from mixture targets of hydroxyapatite and strontium apatite

Sr-substituted hydroxyapatite thin films were prepared by sputtering technique from mixture targets of hydroxyapatite (HA) and strontium apatite (SrAp). The HA and SrAp powders were mixed at 0-100% Sr/(Sr+Ca) target ratios. The coated films were recrystallized by a hydrothermal treatment to reduce film dissolution. The films were then characterized by X-ray diffractometry (XRD), scanning electron microscopy (SEM) and inductively coupled plasma atomic emission spectrometry (ICP). The osteocompatiblity of the films was also evaluated by the size of the bone formation area in osteoblast cells.In the XRD patterns, peaks shifted to lower 2θ values with increasing Sr/(Sr+Ca) target ratios, which indicated Sr incorporation into the HA lattice. In the SEM observation of the hydrothermally treated films, the surface was covered with globular particles, and the size of the globular particles increased from Sr0 to Sr40, and then the size decreased from Sr60 to Sr100. The ICP analysis showed that the Sr/(Sr+Ca) film ratios were almost the same as the target ratios. In the cell culture, the bone formation area on the Sr-substituted HA films increased with increasing Sr concentration, and saturated at Sr60.

Influence of annealing temperature on properties of room-temperature rf-sputtered CuAlOx:Ca thin films

The influence of annealing temperature on the characteristics of rf-sputtered CuAlOx:Ca thin films is studied. Room-temperature sputter-deposited CuAlOx:Ca thin films show an amorphous/nanocrystalline phase with p-type conductivity, as evidenced by Hall measurements and Seebeck coefficient measurements. This film becomes slightly crystalline after annealing at 600°C for 5h in N2 atmosphere. As the annealing temperature is increased to 900°C, crystalline CuAlO2 mixed with CuO and CaAl4O7 are formed in the film; these precipitates extrude and roughen the surface. ZnO:Al/CuAlOx:Ca diodes fabricated using CuAlOx:Ca films that are as-deposited or annealed at 600°C show good rectification characteristics, whereas those fabricated using CuAlOx:Ca films annealed at 900°C show poor diode performance owing to the rugged surface that leads to the poor interface and current leakage paths.

Calcium Thin Film Growth on a Cyano-Substituted Poly(p-phenylene vinylene): Interface Structure and Energetics

The adsorption of Ca on poly[2-(2-ethylhexyloxy)-5-methoxy-1,4-phenylene cyanovinylene] (MEH-CN-PPV) at 130 and 300 K has been studied by adsorption microcalorimetry, X-ray photoelectron spectroscopy (XPS), and low-energy He+ ion-scattering spectroscopy (LEIS). The initial heat of adsorption of Ca on MEH-CN-PPV at 300 K is 436 kJ/mol. The heat of adsorption increases to 464 kJ/mol at ∼0.05 ML. We ascribe this initial heat to Ca abstracting cyano groups from the polymer backbone to make Ca(CN)2 clusters, plus a less important contribution due to Ca abstracting alkoxy groups to make Ca alkoxides. This is supported by XPS which shows the formation of new peaks in the N 1s and C 1s regions consistent with Ca(CN)2. There is also XPS evidence for Ca reacting with some of the ether groups to make Ca alkoxides at low coverage. Above 0.05 ML Ca coverage, the heat of adsorption decreases nearly exponentially to the sublimation enthalpy of bulk Ca solid (178 kJ/mol) by 5 ML. The observed behavior is attributed to the increasing probability of forming Ca nanoparticles and eventually a continuous solid Ca film on top of the reacted polymer. LEIS, which shows only a slow increase of the signal related to solid Ca, supports this model. Incoming Ca atoms undergo a kinetic competition between diffusing into the polymer to react with subsurface cyano or ether groups and forming or adding to three-dimensional Ca clusters on the surface. For studies done at 130 K, similar behavior is observed, with the heat of adsorption starting lower and decreasing more quickly to the heat of sublimation, already by 1.2 ML Ca coverage. This behavior along with the quicker growth of Ca on the surface of the polymer is attributed to the slower diffusion of Ca adatoms to subsurface cyano and ether groups. The effective thickness of “reacted” polymer (i.e., polymer which has lost its −CN groups and some alkoxy groups) is estimated to be 5.6 nm at 300 K but only 1.0 nm at 130 K.

Room-temperature development of thin film composite reverse osmosis membranes from cellulose acetate with antibacterial properties

A cellulose acetate thin film composite (CA TFC) membrane was developed by direct casting of CA onto an ultrafiltration membrane support. The flux through the CA TFC membrane was, as expected, inversely proportional to the selective layer thickness. The membrane with the lowest thickness of the CA film (217nm) initially had poor salt rejection (~55%) but relatively high permeability (~0.5lm−2h−1bar−1). In contrast to asymmetric CA reverse osmosis membranes that are developed in 4°C water baths, the CA TFC membranes were developed by subsequent swelling in room temperature water baths, thermal annealing at 81°C, and with room-temperature incorporation of silver nanoparticles onto CA TFC surfaces by chemical reduction. The change in the physical properties as a result of the swelling process was examined with ellipsometry, grazing incidence X-ray scattering and contact angle measurements. A combined swelling and annealing treatment was found to improve salt rejection to an acceptable reverse osmosis salt rejection level (~94%) without significant deterioration of flux. The swelling time was found to generally improve the membrane performance in terms of flux and surface roughness whilst the silver nanoparticle treatment reduced bacterial surface coverage by four orders of magnitude.

Optimization of Thermal Emittance Tuneability of La (Sr, Ca)MnO<sub>3</sub> Thin-Film Materials in 173-373 K

For the purpose of maximizing the thermal emittance variation of La (Sr, Ca) MnO3 thin films in the temperature range 173-373 K, thin film optical mechanism and mathematical optimization method were used to determine the thin film structure, including substrate type, thin film chemical composition and the optimized film thickness. The optimization results indicate the variation amplitude of La (Sr, Ca) film infrared emittance reaches to 0.62, which is 35% more than that of ceramic type smart radiation materials. The designed thin film structure can be used to enhance the thermal control efficiency of spacecraft greatly.

H2O Vapor Transmission Rate through Polyethylene Naphthalate Polymer Using the Electrical Ca Test

The electrical Ca test was used to measure H2O vapor transmission through polyethylene naphthalate (PEN) polymer with a thickness of 200 μm. On the basis of the time required for the normalized conductance of the Ca film to reach zero, the H2O vapor transmission rate was determined versus H2O flux, temperature, and saturation of the PEN polymer with H2O. The H2O vapor transmission rate was proportional to the H2O flux and only weakly dependent on temperature at constant H2O flux. The transmission coefficient, Γ, for H2O through the PEN polymer at 70 °C was Γ ∼ 3.2 × 10(-10). The corresponding water vapor transmission rate (WVTR) at 70 °C/80% RH was 0.65 g/(m(2) day). The temperature dependence of the H2O vapor transmission rate through PEN at constant H2O flux yielded an activation barrier of E = 12.4 kJ/mol. There was no observable reservoir effect for H2O in the PEN polymer. The H2O vapor transmission rates for initially dry or H2O-saturated PEN polymer substrates were nearly identical at various temperatures. Although the time required for the normalized conductance of the Ca film to reach zero was inversely proportional to the H2O flux, the Ca film conductance did not decrease linearly versus H2O exposure. The Ca film conductance changed very little during initial H2O exposure. This behavior may be caused by the nonlinear oxidation kinetics of the Ca film.

Evaluation of moisture ingress from the perimeter of photovoltaic modules

ABSTRACTMany thin film photovoltaic (PV) technologies can be sensitive to corrosion induced by the presence of water vapor in the packaging materials. Typically impermeable front and backsheets are used in conjunction with an edge‐seal around the perimeter to prevent water vapor ingress. These edge‐seal materials are often made of a polyisobutylene resin filled with desiccant, which dramatically increases the time for moisture to reach sensitive module components. While edge‐seals can prevent moisture ingress, even the lowest diffusivity transparent encapsulant materials are insufficient for the lifetime of a module. To evaluate the performance of edge‐seal and encapsulant materials in a manner that simulates their function in a PV module, an optical method was devised where ingress is detected by reaction of a Ca film with water. Using this method, we have exposed test samples to heat and humidity allowing quantitative comparison of different edge‐seal and encapsulant materials. Next, we use measurements of polymer diffusivity and solubility to evaluate the ability to model this moisture ingress. Here, we find good agreement between these two methods highlighting the much greater ability of polyisobutylene materials to keep moisture out as compared with typical encapsulant materials used in the PV industry. Copyright © 2013 John Wiley & Sons, Ltd.

Evaluation of the sensitivity limits of water vapor transmission rate measurements using electrical calcium test

The development of flexible organic light emitting diode displays and flexible thin film photovoltaic devices is dependent on the use of flexible, low-cost, optically transparent and durable barriers to moisture and∕or oxygen. It is estimated that this will require high barriers with water vapor transmission rates (WVTR) between 10(-4) and 10(-6) g∕m(2)∕day. Thus, there is a need to develop a relatively fast, low cost, and quantitative method to evaluate such low permeation rates. Prior works have demonstrated that Ca films, because they change optically and electrically upon reaction with moisture, can be used as a sensor, enabling one to calculate a WVTR between 10 and 10(-6) g∕m(2)∕day or better. In this work, we analyze the accuracy of an electrical Ca test method. We focus on the effects of the addition of a diffusion spacer and the effects of interactions of edge-seal material with changes to the spacer contacting surface on the overall accuracy. Furthermore, we examine a series of factors that can lead to different errors resulting in qualitative rather than quantitative Ca test behavior. We demonstrate that accurate, relatively high throughput, and reproducible measurements are possible for very low WVTR films in the 10(-6) g∕m(2)∕day range.

The microstructure of multi-layer nc-Ca films on different substrates

Multi-layer nanocrystalline Ca (nc-Ca) films were prepared by vacuum evaporation method, using three different materials as the substrate, namely CaF2(111), Si(100), and Si(111). The films can be stored in the air for a long time, and there was no obvious shedding phenomenon at room temperature. Nc-ca thin films on different substrates were characterised by XRD analysis, showed (111) preferred orientation. On CaF2(111), Si(100) and Si(111) substrates, the average grain size of calcium are 36.8 nm, 43.9 nm and 45.2 nm, respectively. By SEM analysis, there was a better surface morphology of the films on the CaF2(111) substrate.

Evaluating Al2O3 gas diffusion barriers grown directly on Ca films using atomic layer deposition techniques

Al2O3 gas diffusion barriers grown directly on Ca films using atomic layer deposition (ALD) techniques were evaluated using several methods based on Ca oxidation. The Al2O3 ALD films were grown on Ca films at 120 °C using trimethylaluminum and H2O as the reactants. The oxidation of the Ca films was then monitored versus time at 70 °C and ∼28% relative humidity either by measuring the electrical conductance of the Ca film or by recording the photographic image of the Ca film. In the photographic images, the Ca films revealed that the Al2O3 ALD films have a small number of pinhole defects that lead to Ca film oxidation areas that grow radially around the pinhole defect versus time. A burst of new oxidation areas also appeared suddenly at later times and grew radially versus time. This rapid “blooming” may be related to another type of defect caused by water corrosion of the Al2O3 ALD films. In the electrical conductance measurements, the conductance of the Ca film initially showed little change versus time. The conductance then dropped rapidly when the oxidation area in the photographic image was a noticeable fraction of the Ca film area. The conductance measurements yielded a water vapor transmission rate (WVTR) value of ∼2 × 10−2 g/(m2 day) prior to the rapid reduction of the conductance. The photographic images of the Ca film were also analyzed to obtain a WVTR value assuming radial oxidation of the Ca film around defects. The WVTR values obtained from the electrical conductance and the photographic images were in approximate agreement and increased versus Ca film oxidation until the rapid blooming of new circular oxidation areas. The WVTR values are larger than previous measurements and may indicate that Al2O3 ALD films grown directly on Ca are less stable and degraded by Ca film oxidation. This study reveals that a range of WVTR values can be obtained from different variations of the Ca test depending on the extent of Ca film oxidation.

Ca Carboxylate Formation at the Calcium/Poly(methyl methacrylate) Interface

Chemical reactions occurring at the interface during the growth of Ca films on poly(methyl methacrylate) (PMMA) by vapor deposition at room temperature have been investigated in detail by X-ray pho...

Bandgap tuning of MgZnO in flexible transparent n+-ZnO:Al/n-MgZnO/p-CuAlOx:Ca diodes on polyethylene terephthalate substrates

Transparent p–n heterojunctions composed of p-type CuAlOx:Ca and n-type MgZnO thin films are fabricated on indium tin oxide (ITO) coated polyethylene terephthalate (PET) using RF magnetron sputtering at room temperature without additional heat-treatment. The rectifying characteristics of the diodes are observed through the current density–voltage (J–V) curves. The characteristics of the heterojunctions vary with the Mg content in MgZnO. The absolute values of the turn-on voltage and breakdown voltage increase with the Mg content. The diode properties can be designed by adjusting Mg content in the MgZnO layers. The UV responses of the diodes are evaluated by measuring the J–V characteristics under UV irradiation at a wavelength of 365nm. The absorption decreases with an increase in the Mg content in the diodes. The results show that these transparent diodes can be used as UV detectors on plastics.